The invention relates to a water-tight bore shaft foundation.
In shafts which are manufactured in accordance with the freezing procedure, various solutions for mining-insensitive foundations are known. However, these solutions cannot be used in bore shafts because in bore shafts the foundation area is not accessible.
Foundations which have been known in the past for bore shafts are connected to the ground and, therefore, are mining-sensitive. In these foundations, after the shaft bore has been finished, the outer tight shaft structure is lowered as a pontoon by means of ballast water and its own weight until the intended end position is reached. In this end position, the lower end of the shaft structure is surrounded with a base which is made of underwater concrete introduced between the ground and the shaft structure. After the underwater concrete has hardened, the annular space between the shaft structure and the ground above the base is filled with soft asphalt which displaces the drilling liquid in the annular space. The disadvantage of such a bore shaft foundation is the fact that the lower end of the shaft structure is mounted rigidly, so that mining movements of the ground--possibly in conjunction with inclinations of the shaft structure relative to the shaft axis--may irreparably damage the bore shaft foundation and, thus, the bore shaft foundation may leak.
The invention is based on the problem of constructing a water-tight bore shaft foundation according to the features in the preamble of claim 1 in such a way that mining movements of the ground no longer can have a negative influence on the water-tight quality of the bore shaft foundation, even if substantial curvatures of the shaft axis occur.
Thus, the shaft structure is now placed with its lower end on a liquid and is on the outside surrounded completely by liquid. The hydraulic thrust bearing absorbs the vertical loads, while the circumferential hydraulic annular cylinder carries out the yielding and tightening functions. These two elements form an articulated arrangement which makes it possible for the shaft structure to tilt by up to 2% of inclination change relative to the base, without impairing the water tightness of the bore shaft foundation. In addition, the bore shaft foundation is free of rearrangements of forces.
The hydraulic thrust bearing serves for the permanent transmission of the own weight of the shaft structure through the base into the ground. The hydraulic medium in the thrust bearing is subjected to a pressure which corresponds to the own weight of the shaft structure, independently of the state of tilting of the shaft structure which may occur due to mining influences. Consequently, vertical pressures distributed over the circumference are uniformly transmitted into the ground in any tilting state. In this manner, the load acting on the ground as well as on the shaft structure is kept as low as possible. The hydraulic annular cylinder which surrounds the lower vertical portion of the shaft structure seals the bore shaft in a yielding manner relative to the base. It is of significance in this connection that the annular cylinder extends to a sufficient extent upwardly along the shaft structure from the thrust bearing into the annular space with the soft asphalt. As a result, this asphalt can transmit its hydraulic pressure continuously on the hydraulic medium in the annular cylinder.
The features of the invention make it possible to support a shaft structure for a bore shaft completely slidingly in the water-tight portion. This provides the advantage that any damage in the non-water-tight, ground-connected shaft structure underneath the tilting joint arrangement can be repaired relatively easily from the hollow space of the bore shaft. Therefore, such a mining-insensitive shaft structure for bore shafts which is mounted slidingly in a water-tight manner, makes it possible to arrange bore shafts even in mining areas with significant mining influences in order to supply these mining operations with fresh air.
The thrust bearing cushion preferably has an oval cross-section with a flat upper side which is in contact with the lower end face of the shaft structure and has a flat underside which is in contact with the base. The width of this oval cushion is adapted to the wall thickness of the shaft structure. Its height is between 100 and 200 mm. The walls of the cushion can be provided with a statically sufficient thickness. The cushion is filled with a non-corrosive medium, so that corrosion of the steel skin of the cushion can be excluded.
As already mentioned above, vertical pressures from the own weight of the shaft structure are uniformly conducted into the ground through the thrust bearing and the base. Horizontal transverse forces resulting from the curvature of the shaft axis are transmitted through friction and adherence from the shaft structure to the flat upper side of the cushion. The transverse forces are conducted through shear stresses from the other side through the radially inner and outer curved connecting portions to the flat underside of the cushion and are conducted from there into the ground. The cushion is constructed in such a way that it is continuously capable of absorbing annular tension stresses from the pressure of the hydraulic medium. When the cushion is welded together from various sheet metals, the welding seams must be adapted to these annular tension stresses.
The thrust bearing may be connected with the lower end face of the shaft structure.
As far as the circumferential annular cylinder of the hydraulic tilting joint arrangement is concerned. As is the case in the thrust bearing, this annular cylinder also is a hollow steel body which is closed to all sides and is filled with liquid. The annular cylinder which has the shape of a circle in horizontal cross-section has a radial thickness of about 100 mm to 200 mm and has to be constructed with a height of only a few meters and may be provided with a relatively thin outer steel jacket which is tightly connected to the outer wall of the shaft structure. The annular cylinder extends beyond the annular portion of the base which surrounds the shaft structure into the soft asphalt thereabove to such an extent, but at least by 1 m, that the hydraulic pressure of the asphalt in the annular space between the ground and the shaft structure is transmitted through the relatively thin steel jacket of the annular cylinder to the hydraulic medium in the annular cylinder. Consequently, tilting of the shaft structure results also in a tilting of the outer wall of the annular cylinder and, thus, leads to flowing of the hydraulic medium in the annular cylinder.
Although the thrust bearing and the circumferential annular cylinder may be filled with different hydraulic media, the thrust bearing and the annular cylinder are filled with a viscous mixture of lime dust, fine sand and bitumen.